Riser Weak Link Pressure Balancing and Damping
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Solution Overview
Problem
Conventional weak links for riser systems in hydrocarbon exploration lack effective pressure balancing and damping mechanisms, leading to uncontrolled separation and potential damage during emergency disconnection scenarios, and fail to adapt to varying operational conditions such as subsea operations and heavy equipment deployment.
Innovation Solution
A weak link system incorporating a pressure balancing mechanism with pistons and a damping mechanism using seawater-filled cylinders for controlled separation, along with a strong mode mechanism to increase gripping force, ensuring predictable and safe disconnection and connection operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional weak link uses tension bolts to connect flanged sections, then the connection is simple and easy to manufacture, but the separation becomes uncontrolled due to end cap pressure effects causing potential damage and safety risks
Solution Approach 1:
A pressure balancing mechanism is introduced as an intermediary component between the flanged sections and the tension bolts. This mechanism includes pressure balancing pistons that transfer internal pressure loads to the flanged sections, counteracting the end cap effect on the bolts. By mediating the pressure forces, the bolts experience only the predefined tension load, enabling controlled separation at the intended failure point without uncontrolled recoiling or damage.
Solution Approach 2:
The weak link is segmented into distinct functional components: flanged sections for connection, tension bolts for controlled failure, and a separate pressure balancing mechanism. This segmentation allows each component to perform its specific function - the bolts fail at predefined tension while the pressure balancing mechanism independently manages the internal pressure loads, preventing interference between these functions.
2Reliability
If the weak link is designed to fail at a given load to enable passive disconnection, then safety is improved, but the end cap effect causes varying pre-tension on bolts making the failure load unpredictable
Solution Approach 1:
The pressure balancing pistons act as intermediaries that transfer the internal pressure loads directly to the flanged sections. This mediation ensures that the tension bolts are subjected only to the predefined operational tension load, not the varying end cap pressures. Consequently, the failure load becomes predictable and consistent, occurring at the predefined tension threshold regardless of internal pressure variations.
3Reliability
If a weak link is used to protect against over-pull and buckling, then subsea system safety is improved, but the link may fail due to compensator lock up rather than intended overload conditions
Solution Approach 1:
The weak link exhibits different local mechanical properties through its two operational modes. In strong mode, the flanged sections are tightly clamped together with high friction, enabling the link to withstand buckling and over-pull forces. In weak mode, the connection is less restrictive, allowing controlled separation at predefined tension. This local quality differentiation enables the link to respond appropriately to different failure conditions - resisting compressive over-pull while allowing tensile separation.
4Strength
If the gripping force between flanged sections is increased to prevent accidental separation, then connection strength is improved, but the ability to fail at predefined load is reduced
Solution Approach 1:
The weak link employs dynamic characteristics through friction-based connection. The gripping force is sufficient to prevent accidental separation under normal conditions but allows controlled failure when the predefined tension threshold is exceeded. The friction between flanged surfaces provides a dynamic response - maintaining strength below the failure threshold while enabling predictable separation above it, without requiring mechanical locking mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides controlled and predictable separation of riser components, reducing the risk of damage to subsea infrastructure and personnel, while maintaining operational reliability under varying conditions, including subsea operations and heavy equipment handling.
Implementation Method 1
a pressure balancing mechanism is provided, for balancing axial forces acting on said connection means due to end cap effect of said riser system
Implementation Method 2
The weak link according to the present invention can also effectively function in both weak mode and strong mode as explained before, in a very simple manner
Data Source
AI summary
A weak link (17, 43) for a riser system comprising a pin (2, 25) and a box (1, 24), bolts (11, 34) for releasably connecting the pin (2, 25) and the box (1, 24), the bolts being designed to break at a predefined tension. The link further comprising a pressure balancing mechanism for balancing axial forces acting on the bolts (11, 34) due to end cap effect. The weak link also comprises a strong mode mechanism and a dampening mechanism.